The present invention relates to a secondary battery such as a lithium ion secondary battery, which is provided with a battery protection device inside of the battery and which has thereby functions for protecting the battery from overcharging and over-discharging, etc., in the battery itself.
Various kinds of protective features are built into secondary batteries in order to protect against shorts in battery peripheral circuits in equipment wherein such secondary batteries are used, against shorts between positive and negative electrodes, and against battery damage resulting from abnormal usage as in overcharging or over-discharging. These include PTC elements for blocking excessive discharge currents caused by shorts and the like, and safety valves and the like which interrupt the conducting circuit by the anomalous rises in internal battery voltage associated with overcharging and release that internal voltage. These protective features are commonly known as features wherewith the secondary battery itself is provided. In lithium ion secondary batteries, moreover, protective circuits are provided for preventing overcharging and over-discharging. These protective circuits are generally contained inside a battery pack case and integrated with the lithium ion secondary battery. As well known, such battery pack constructions wherein the battery and the protective circuit are accommodated and integrated in a case are widely used as battery power supplies in portable telephone instruments and mobile computers, etc., that use lithium ion secondary batteries.
The protective circuits described above can also incorporate excessive current interrupting features and battery temperature monitoring features and the like in addition to features for preventing overcharging and over-discharging as described in the foregoing. If these features can be built into the secondary battery itself, it will be no more necessary to construct the battery pack and secondary batteries with protective circuits can be provided for general purposes. Japanese Laid-Open Patent Application No. 8-31460 discloses a battery which is though to have been developed for the purpose of accommodating a protective circuit inside the battery. In this art, a protective circuit and other constituent elements are arranged in an upper part of the battery, and the protective circuit, and the battery, are accommodated inside an outer case. Thus it is nothing different from the conventional battery pack construction. What is demanded in a secondary battery provided with a protective circuit is one which has roughly the same dimensions and shape as a conventional secondary battery having no- protective circuit, with the protective circuit accommodated inside that battery case.
The inventors of the present invention developed a secondary battery having a protective circuit accommodated inside the battery, along the lines described in the foregoing, and proposed that secondary battery in Japanese Laid-Open Patent Application No. 8-178896. One embodiment thereof is diagrammed in FIG. 37. Therein, a battery protection device containing the protective circuit described earlier is arranged in a sealing member 90 that seals the open end of a battery case accommodating electricity generating elements.
The battery protection device within the sealing member 90 comprises a circuit board constituting an electronic circuit 77 forming a protective circuit, a PTC element 72 that is a critical temperature resistor for blocking excessive currents such as occur with shorts, etc., and a current interrupting mechanism 73 that interrupts the conducting circuit by breaking when the voltage inside the battery rises abnormally thereby to release the abnormal internal voltage. The positive terminal of the electricity generating elements is connected to the circuit board through the current interrupting mechanism 73 and the PTC element 72, and electrical connections are effected from the circuit board to a positive terminal cap 75 that constitutes the positive terminal of the battery, and to an S pole cap 76 that is for externally connecting the minus side of the electronic circuit 77.
The construction described in the foregoing is diagrammed in schematic form in FIG. 38. The electronic circuit 77 is made up of a battery protection IC 80 comprising overcharging and over-discharging control functions, and an FET 81 for turning on and off the conducting circuit on the positive terminal side by control signals from the battery protection IC 80. The negative terminal side of this electronic circuit 77 is electrically connected to the S pole cap 76. Therefore, when this secondary battery is installed in equipment wherein it is used or in a charger, an electrical connection is effected across the S pole cap 76 and a battery case 83 constituting the negative terminal of the secondary battery, thereby putting the electronic circuit 77 in an operating state. When this secondary battery is not installed in equipment, no power consumption arises because of the electronic circuit 77, although it is very slight. As diagrammed, the current interrupting mechanism 73, PTC element 72, and electronic circuit 77 are arranged in series in the conducting circuit on the positive terminal side from the electricity generating elements 78. Thus the secondary battery is equipped with three levels of battery protection features.
However, when the resistance value of the PTC element 72 secured by caulking inside the sealing member 90 rises by self-heating due to excessive currents, the cubic volume thereof expands when a tripped state is reached. When this cycle of expansion and return to normal is repeated again and again, the caulking becomes loosened so that a very small gap develops, leading to the problem of electrolyte leaking out through the gap.
There is also another problem in that, because the circuit board is arranged in proximity to the current interrupting mechanism 73, limitations are placed on the space available for deformation of the current interrupting mechanism 73 which will deform and rupture due to abnormal rises in the internal battery voltage, making it difficult to obtain deformation/rupture precision.
An object of the present invention is to provide a secondary battery wherein a battery protection device comprising a protective circuit is accommodated inside the battery, wherewith there is but slight change in the size of the battery, and wherewith battery performance is not compromised.
A first aspect of the present invention is a secondary battery wherein electricity generating elements are accommodated inside a battery case formed in a cylindrical shape having a bottom, the open end of the battery case being sealed by a sealing member having a battery protection device built therein, characterized in that the battery protection device comprises a protective circuit, for protecting the battery from overcharging and over-discharging, consisting of an electronic circuit formed on a circuit board, the circuit board being arranged in the sealing member such that an electrode terminal formed in one side thereof is exposed to the outside.
According to this construction, the protective circuit is built into the secondary battery itself, in which the protective circuit is arranged inside the sealing member, and the electrode terminal passed through the electronic circuit forming this protective circuit is attached so that it is externally exposed. Thus the secondary battery is constructed with a protective circuit without resorting to the construction of a battery pack. Battery damage caused by equipment malfunction or abnormal use is prevented by the features provided in this protective circuit for preventing overcharging, over-discharging, and excessive discharge current, etc.
A second aspect of the present invention is a secondary battery wherein electricity generating elements are accommodated inside a battery case formed in a cylindrical shape having a bottom, the open end of the battery case being sealed by a sealing member having a battery protection device built therein, characterized in that the battery protection device comprises a protective circuit, for protecting the battery from overcharging and over-discharging, consisting of an electronic circuit formed on a circuit board, the circuit board being arranged in the sealing member such that an electrode terminal formed in one side thereof is exposed to the outside, and a current interruption means for interrupting a conducting circuit when the internal battery voltage rises abnormally and for discharging the internal voltage.
According to this construction, the protective circuit is built into the secondary battery itself, by arranging the protective circuit and current interruption means inside the sealing member. Thus the secondary battery is constructed with a protective circuit without resorting to the construction of a battery pack. Furthermore, since the conducting circuit is interrupted by the current interruption means even when the protective circuit is damaged, battery damage caused by equipment malfunction or abnormal use is prevented.
A third aspect of the present invention is a secondary battery wherein electricity generating elements are accommodated inside a battery case formed in a cylindrical shape having a bottom, the open end of the battery case being sealed by a sealing member having a battery protection device built therein, characterized in that the battery protection device comprises a protective circuit, for protecting the battery from overcharging and over-discharging, consisting of an electronic circuit formed on a circuit board, the circuit board being arranged in the sealing member such that an electrode terminal formed in one side thereof is exposed to the outside, an excessive current blocking means for blocking current conduction when excessive current is discharged such as when there is a short, etc., and a current interruption means for interrupting the conducting circuit when the internal battery voltage rises abnormally and for discharging the internal voltage.
According to this construction, threefold battery protection features are built into the secondary battery itself, by providing a protective circuit, excessive current blocking means, and current interruption means inside the sealing member. Thus the secondary battery itself can be provided with a battery protection device without resorting to the construction of a pack battery or the like.
In the construction described above, the excessive current blocking means can employ a PTC which heats by excessive current and restricts discharge of the current by a rapid increase in the resistance value.
Furthermore, when a feature for detecting and interrupting excessive current is constructed in the protective circuit, the PTC can be eliminated, in which case a metal ring can be arranged in place of the PTC.
The circuit board constituting the protective circuit comprises a positive electrode terminal of said battery formed in center portion on one surface side, an externally connecting electrode terminal that becomes a grounding site in said protective circuit formed in peripheral portion on said one surface side, a positive terminal connecting electrode connecting to positive terminal of electricity generating elements formed in peripheral portion of other surface side, and through holes provided at prescribed positions for making connections between said one surface side and said other surface side. The other side of the circuit board is arranged so that it is exposed to the outside from the sealing plate, wherefore the positive electrode terminal functions as the positive terminal of the secondary battery. The protective circuit is activated by connecting the externally connecting electrode terminal to the battery case. that forms the negative terminal.
The electrode terminals can be constituted by mounting metal plates on a conductor pattern on the circuit board by solder welding or with a conductive adhesive. Welding of such metal plates facilitates electrical connection of the secondary battery to the equipment side.
Further, the metal plate, which is bonded to the positive electrode terminal, may be formed with a projection in the central portion on the outer side thereof, so as to achieve better contact connection with the connecting terminals on the equipment. This can also improve weldability of leads when joining them thereto because of the concentration of welding current toward the projection in resistance welding.
Moreover, by forming the metal plate from nickel plate, or gold-plated metal plate, or metal plate of the same material as the battery case, the ability to withstand repeated contact can be enhanced in the case of the nickel plate, outstanding corrosion resistance can be effected in the case of the nickel plate or gold-plated metal plate, and a reduction in contact resistance can be realized with the gold-plating. By employing the same material as the battery case, the welding conditions in resistance welding also become easier when effecting series connections.
The circuit board is supported by a supporting member that is electrically connected to the positive terminal of the electricity generating elements and secured inside the sealing member on the outer circumferential side, so that this supporting member and the positive terminal connecting electrode make contact on the inner circumferential side thereof. Further, the supporting member and the positive terminal connecting electrode are bonded together, by soldering or an electrically conductive adhesive. Thereby, electrical connection to the protective circuit is made simultaneously with the attachment to the sealing member of the circuit board.
A circuit board positioning projection may be provided on the supporting member, whereby not only will the process of attaching to the circuit board be made easier, but positioning in the connecting position will also be made easy.
Furthermore, by covering the electronic circuit portion of the protective circuit with a resin, the moisture resistance of the electronic circuit portion and resistance to corrosion from the electrolyte components can be enhanced.
Furthermore, by providing an electrically conducting member for making an electrical connection between the battery case constituting the negative terminal of the battery and the externally connecting electrode terminal on the circuit board, the protective circuit is constantly kept in an energized state. Accordingly, connecting members and other constituent elements for connecting the externally connecting electrode terminal to the negative terminal when the battery is installed in equipment can be eliminated. Self-discharge loss caused by always conducting current in the protective circuit during prolonged storage is not a problem because, as with conventional battery pack constructions, the battery will be charged prior to use in the equipment, either by the equipment or with a charger.
The electrically conducting member described above may be provided with openings in the peripheral portion and center portion of the bottom surface, and formed in the shape of a cylinder having a bottom with an inner diameter that will fit onto the open end of the battery case. By fitting it to the open end of the battery case, electrical connection can be effected between the externally connecting electrode terminal on the circuit board, so that a stabilized fitting condition is realized. By joining the electrically conducting member and the externally connecting electrode terminal by soldering or an electrically conductive adhesive, the electrical connection can be made more stable.
It is preferable to form the electrically conducting member of a resilient metal material, or of a metal material exhibiting outstanding weldability with the battery case, or of the same metal material as the battery case. With the resilient metal material, the electrically conducting member can be pressed against the battery case and the electrical connection is stabilized. When the electrically conducting member and the battery case are joined by welding, it is beneficial to use a metal material having outstanding weldability. If the same metal material as the battery case is used, weldability will also be assured.
The electrically conducting member can be formed so that the surface portion of the bottom surface thereof, excluding the peripheral portion thereof, is given an insulating coating. While the peripheral portion of the bottom surface functions as a minus electrode terminal, and together with the positive electrode terminal as seen from the opening in the center portion, positive and negative input/output terminals can be provided in surfaces in the same direction in the battery. The battery connection structure of the equipment is thereby simplified. The insulating coating noted above functions as an insulating portion between these positive and negative terminals.
Alternatively, a connecting member joined to the externally connecting electrode terminal may be provided, this being electrically connected to the open end of the battery case, to which the sealing member is secured by caulking. The externally connecting electrode terminal can thereby be connected to the battery case without using an electrically conducting member.
A securing member is secured inside the sealing member together with a supporting member on an outer circumferential side thereof, and faces said supporting member on an inner circumferential side thereof, with the circuit board being interposed therebetween, and said securing member and said supporting member are fastened together at a plurality of positions in a peripheral portion of said circuit board with fastening means. By providing such a construction, the peripheral portion of the circuit board will be held from both sides, wherefore a strong securing structure can be obtained.
The fastening means can be formed by resin rivets, of which ends are passed through the supporting member, circuit board, and securing member and are melt-molded. Since fastening is done using insulating resin rivets, both sides of the circuit board can be fastened with reliable electrical insulation therebetween.
The fastening means can be formed with metal members that are passed through the securing member and the circuit board with an intervening insulating material and secured to the supporting member. The circuit board can thereby be attached to the sealing member after securing the sealing member to the battery case, and the process of caulking the sealing member to the battery case can be performed easily.
Openings are formed in a prescribed constituent member of the sealing member, which openings open toward the exterior in a direction perpendicular to the cylinder direction of the battery case. When gas pressure that has abnormally risen inside the battery is exhausted, the danger of the battery flying out in conjunction with the exhausting of the gas can be prevented because the openings are formed in a direction perpendicular to the gas blowout.
The surface of the battery case is coated with an insulating coating that leaves an exposed surface larger than the outer dimensions of the positive electrode terminal in the center portion of the bottom surface, and an exposed surface at a prescribed circular place in the lateral circumferential surface. The insulating coating on the bottom surface functions as an insulating layer with another battery when connected in series, and the exposed surface in the circular place can effect a minus connection to the battery case in the lateral circumferential surface.
A recessed part having a diameter larger than the external dimensions of the positive electrode terminal may be formed in the center portion of the bottom surface of the battery case. That way, when batteries are connected in series, the positive electrode terminal of the other battery will fit into the recessed part and be held in position.
A fourth aspect of the present invention is a secondary battery wherein electricity generating elements are accommodated inside a battery case formed in a cylindrical shape having a bottom, an open end of said battery case being sealed with a sealing member comprising a battery protection device therein, characterized in that: a circuit board having a protective circuit constructed on an inner surface side thereof for protecting battery from overcharging and over-discharging, is arranged in an outermost part of said sealing member; a positive input/output terminal connected via said protective circuit to a positive terminal plate is joined to an outer surface side of said circuit board, in center portion thereof; and an outer cap which covers a peripheral portion of said circuit board is fit onto said battery case and joined thereto.
According to this construction, the secondary battery has a circuit board constituting a protective circuit arranged in the sealing member, and the positive terminal plate of the secondary battery is connected to the positive input/output terminal through the protective circuit. Therefore the secondary battery is protected from overcharging and over-discharging, etc., by the protective circuit. There is no need to construct a battery pack in which the secondary battery and the protective circuit are accommodated inside a pack case. The provision of a protective circuit is an essential requirement for lithium ion secondary batteries, and if the secondary battery itself can have the protective circuit, it can be widely used for general purposes. Moreover, the equipment employing the batteries can be constructed compactly.
In the construction described in the foregoing, a temperature detector terminal is provided on the outer surface side of the circuit board, and a temperature detector element for detecting the temperature of the protective circuit and the battery, connected thereto, is provided, so that the temperatures of the protective circuit and battery are output to the temperature detector terminal. Hence the equipment using the battery or a charger can detect the battery temperature condition from the temperature detector terminal, whereby utilization at proper temperatures can be realized.
The sealing member comprises a current interruption means formed in a disk shape, a PTC formed in a circular ring shape, and an inner cap formed in a cap shape open in the center portion, stacked together, respectively having the outer circumferential portions thereof sandwich-secured by the outer circumferential portion of the sealing bottom plate with an intervening inner gasket. A spot ring attached to the circuit board is joined to the apex of the inner cap, thus providing a protective circuit. The sealing member is secured by caulking to the open end of the battery case with an intervening outer gasket. Thereby, the current interruption means, the PTC for blocking excessive discharge currents, and the protective circuit can be constructed inside the sealing member. Thus safety is enhanced when the secondary battery is abnormally used or the equipment malfunctions, by means of a plurality of battery protection devices.
The spot ring is attached to the circuit board by joining the ring-shaped surface to the conductor pattern formed on the circuit board. The circuit board is secured to the top of the inner cap by joining to the inner cap a joining surface of the spot ring that protrudes from the ring-shaped surface to the outside of the circuit board. Thereby the attachment operation of arranging the circuit board in the sealing member can be performed easily.
The spot ring should preferably be formed of a copper-nickel alloy or of a clad metal containing a copper-nickel alloy, which exhibits superior weldability, electrical conductivity, and corrosion resistance.
An IC component is mounted on an IC heat-radiating conductor pattern formed on the inner surface side of the circuit board. A negative terminal connecting conductor pattern on the outer surface side to which the outer cap is joined and the IC heat-radiating conductor pattern are connected by through holes. A temperature detector element is arranged between the negative terminal connecting conductor pattern and a temperature detector element connecting conductor pattern. Heat from the IC component is conveyed from the IC heat-radiating conductor pattern to the negative terminal connecting conductor pattern, and the heat in the battery case is also conveyed from the outer cap to the negative terminal connecting conductor pattern. Therefore the temperature detector element connected to the negative terminal connecting conductor pattern will be changed by the heat from the IC component and the battery case. Changes in this temperature detector element can be detected from the temperature detector terminal joined to the temperature detector element connecting conductor pattern, wherefore the IC component and the battery can be used at suitable temperatures.
A solder resist is arranged at prescribed places excluding critical parts of the circuit board, such that the solder resist is arranged in a plurality of island-shaped patterns arrayed in the positions of the IC component on the IC heat-radiating conductor pattern. The IC component is mounted on the island-shaped patterns by filling the island-shaped solder resist array intervals with a adhesive. That way, the IC component can be insulated from the conductor pattern by the solder resist, and, since the area of the solder resist of low thermal conductivity is small, the heat from the IC component can be conveyed to the IC heat-radiating conductor pattern by the adhesive filled therebetween.
The island-shaped solder resist may be arranged such that the sides of hexagonal island-shaped patterns are aligned in parallel at a prescribed interval. The island-shaped patterns can thereby be arranged uniformly, thus obtaining suitable adhesive filling spaces therebetween.
The temperature detector terminal and the positive input/output terminal can be formed in a metal part wherein said temperature detector terminal in center thereof and positive input/output terminal formed so as to surround said temperature detector terminal at an interval are coupled and integrated by a thin bridge by metal molding, the interval between said temperature detector terminal and said positive input/output terminal being filled with an insulating resin to join both together, after which said bridge is cut away to form a coupled and integrated complex terminal. The temperature detector terminal and the positive input/output terminal can be constructed as an integrated complex terminal insulated by the insulating resin, and the attachment to the circuit board can be performed simultaneously.
The temperature detector terminal can be formed so that the apex thereof is positioned lower than the positive input/output terminal. When temperature detection is performed by separate means, by connecting a plate-shaped connector to the positive input/output terminal, provision can be made so that the temperature detector terminal is not used. Also, when this secondary battery is connected in series and constructed in a battery pack, temperature detection means can be provided as a battery pack, the positive input/output terminal can be made to conduct by contact with the bottom of the battery case, and the temperature detector terminal can be disabled.
The outer cap may be formed, of metal material, in a cylindrical shape having a bottom, provided with a cylindrical part that fits with the circumferential side surface of the battery case and a bottom surface part open in the center part thereof. In the bottom surface part thereof, a negative terminal connecting piece that connects to a negative terminal connecting conductor pattern formed on the circuit board, a board clamping piece that presses the outer surface side of the circuit board, and an upper surface piece that is positioned at a lower height than the board-clamping piece are formed. A resin molded part is formed which covers the outer surface side of the circuit board, excluding the temperature detector terminal and the positive input/output terminal, exposing the negative terminal connecting piece and the upper surface piece. The battery case that is the negative input/output terminal can be connected to the circuit board and, together therewith, the peripheral portion of the circuit board positioned in the outermost part of the sealing member can be coated with the resin molded part to prevent damage to the circuit board.
When a ring-shaped rib is formed in the resin molded part, short prevention between the negative terminal connecting piece and the positive input/output terminal in the center portion is optimized.
The outer cap should preferably be formed of a metal material, using either a copper-nickel alloy or a clad metal containing a copper-nickel alloy, which exhibits outstanding weldability, electrical conductivity, corrosion resistance, and strength.
A metal ring can be provided in place of a PTC. Because it is possible to incorporate functions in the electronic circuit on the circuit board for detecting excessive currents and interrupting the conducting circuit, the PTC constituting excessive current blocking means can be eliminated. When the PTC is replaced by a metal ring, the problems caused by PTC expansion are done away with. By eliminating the PTC, furthermore, the resistance value of the conducting circuit is reduced, contributing to a decrease in the internal resistance of the battery.